1. Field of the Invention
The present invention relates to a wheel pressure-reduction determining system for a vehicle for determining a reduction in pressure in a tire based on a difference in diameter between follower and driven wheels.
2. Description of the Related Art
A traction control system or an antilock brake system in a vehicle includes rotation-number sensors in the follower and driven wheels to detect follower wheel speeds and driven wheel speeds used for calculation of a slip rate of a wheel, or the like. However, if the tire is reduced in diameter due to a reduction in tire pressure, the numbers of rotations of the follower wheels and of the driven wheels detected by the rotation-number sensors do not correctly correspond to the follower wheel speeds and the driven wheel speeds.
Therefore, in a conventional system, a difference between the left and right follower wheel speeds is compared with a difference between the left and right driven wheel speeds. If the difference between the left and right follower wheel speeds is larger than the left and right driven wheel speeds, it is determined that a reduction in diameter due to a reduction in tire pressure has been produced in any of the follower wheels. If the difference between the left and right driven wheel speeds is larger than the difference between the left and right follower wheel speeds, it is determined that a reduction in diameter due to a reduction in tire pressure has been produced in any of the driven wheels.
However, the above prior art technique has the following problem: When a difference is produced between slipping states in the wheels, for example, because of unbalanced depths of the tires of the left and right driven wheels, it is impossible to discriminate a difference between the left and right driven wheel speeds due to the difference between the slipping states from a difference between the left and right driven wheel speeds due to the reduction in diameter caused by the reduction in tire pressure. Therefore, it is impossible to precisely detect the reduction in diameter caused by the reduction in tire pressure in the tire.
The present invention has been accomplished with the above circumstances in view, and it is an object of the present invention to provide a wheel pressure-reduction determining system for a vehicle, wherein a reduction in pressure in the follower wheels and the driven wheels can be precisely determined irrespective of slipping states of the driven wheels.